Prof Jennie Brand-Miller answers your questions.
Can you explain the difference between glycemic index, glycemic load and glycemic response?
Glycemic Index (GI) is a measure of the quality of carbohydrate. It compares carbohydrates, gram for gram, in one food versus another. Different carbohydrate foods can behave quite differently in your body. Some break down quickly during digestion and release glucose rapidly into the bloodstream; others break down gradually as you digest them and slowly trickle glucose into the blood stream. The glycemic index or GI, a relative ranking on a scale of 0 to 100, is how we describe this difference. After testing hundreds of carbohydrate foods around the world, scientists have found that foods with a low GI will have less effect on your blood glucose than foods with a high GI. High GI foods tend to cause spikes in your glucose levels whereas low GI foods tend to cause gentle rises. To make a fair comparison, all foods are compared with a reference food and tested following an internationally standardised method.
Glycemic Load (GL) is a measure of both the quality and quantity of carbohydrate. How high your blood glucose actually rises and how long it remains high when you eat a meal containing carbohydrate depends on both its GI and the amount of carbohydrate in the meal. Researchers at Harvard University came up with a term to describe this: glycemic load. It is calculated by multiplying the GI of a food by the available carbohydrate content (carbohydrate minus fibre) in the serving (expressed in grams), divided by 100. GL = GI/100 x available carbs per serving. GL per 1000 kJ has been shown to be the single best predictor of actual glycemic responses to single foods and mixed meals.
Glycemic response or glycemic impact describes the change or pattern of change in blood glucose after consuming a food or meal. Glucose responses can be fast or slow, short or prolonged, high or low. The glycemic response varies from person to person, depending on their 'glucose tolerance'. A person with diabetes or impaired glucose tolerance will have a higher glycemic response to any food than a lean, young, healthy individual. Nonetheless, in a single individual, we can reliably predict that a low GI/GL meal will produce a lower glycemic response than a high GI/GL meal.
GI testing by an accredited laboratory
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 Canada
Phone +1 416 861 0506
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022